This section is from the book "Anatomy Of The Arteries Of The Human Body", by John Hatch Power. Also available from Amazon: Anatomy of the Arteries of the Human Body, with the Descriptive Anatomy of the Heart.
Anteriorly, in addition to the integuments and pectoralis major, it is covered more immediately by the pectoralis minor muscle, and about the middle of this stage by a portion of the superior trunks of the brachial plexus of nerves, in which situation the plexus forms a complete sheath around the artery. Posteriorly it corresponds to a quantity of areolar tissue lying between the artery and sub-scapularis muscle. Externally it is related to the upper part of the insertion of the sub-scapularis tendon into the lesser tuberosity of the humerus, and partly to the brachial plexus. Internally we find the axillary vein and some areolar tissue separating it from the serratus magnus.